This invention relates to radio transceivers. In particular, it relates to a method and means of using a fully synchronized programmable counter with a near 50% duty cycle output signal as a frequency divider to provide electronic bandswitching as well as channel frequency selection for a transmitter and receiver path in a radio transceiver.
Two-way radio communications are generally carried out using an associated pair of frequencies within one or more bands. (Such pairs are often referred to as a "channel"). Thus, when a transceiver operates in a particular channel, it must generate at least one frequency for transmission and at least one frequency with which to mix a received signal to produce a fixed intermediate frequency signal.
Modern communication systems require more efficient use of the limited and congested radio spectrum, and therefore utilize high-speed data and elaborate signalling schemes to achieve greater message signal throughput. Such signalling schemes, however, demand better performance from the transmitter and receiver when changing modes between transmit and receive, and when changing between channels. These radios must achieve phase-lock quickly and must maintain an accurate carrier frequency with low-noise, and minimal jitter.
despite this need, however, radios have historically been configured to cover relatively narrow bands of frequencies, say 45-50 MHz, or about 10% bandwidth. Today, however, there is a need to switch across wider bands of frequencies. This presents particularly difficult design problems, whether attempting to operate at lower carrier frequencies, such as 30-50 MHz (low-band), or between different bands (i.e., low-band and 150 MHz, high-band). This is because, by conventional methods, the radio's VCO must cover almost an octave of frequencies. In addition, the design and construction of such a VCO operating at a low frequency is made more difficult when wide modulation bandwidth and low-noise performance are needed simultaneously. Thus, conventional VCOs are limited to a specific, narrow range of frequencies or are otherwise compromised in overall performance, particularly for mobile radio applications.